Difference Between Mitosis And Meiosis

Difference Between Mitosis And Meiosis

In single celled organisms cell reproduction gives rise to the next generation. In multicellular organisms cell division occurs not just to produce a whole new organism but for growth and replacement of worn out cells within the organisms. Cell division is always highly regulated and follows a highly orchestrated series of steps. The term cytokinesis refers to dividing a cell in half, while mitosis and meiosis refer to two different forms of nuclear division. Mitosis results in two nuclei that are identical to the original nucleus. Meiosis on the other hand results in four nuclei that each have ½ the chromosomes of the original cell. In animals meiosis only occurs in the cells that give rise to the sex cells (gametes), i.e., the egg and the sperm.

Difference between Mitosis and Meiosis

Types

Mitosis

Meiosis

Interphase

Interphase – DNA has been replicated but Chromosomes not yet visible

Each chromosome replicates.The result is two genetically identical sister chromatids

Prophase

Prophase – Chromosomes condense and thicken, Each duplicated chromosome appear as two identical sister chromatids, The mitotic spindle begins to form

Prophase I (Crossing-over recombination) Homologous chromosomes (each consisting of two sister chromatids) come together as pairs The structure formed is called a tetrad. Chromosome segments are swapped between non-sister chromatids at crossover points called chiasmata (= crossing-over)

Metaphase

Metaphase -The chromosomes assemble at the equator = metaphase plate

Metaphase I Chromosomes align on the metaphase plate. Chromosomes still arranged as: pairs of homologues

Anaphase

Anaphase – The spindle fibres begin to contract. This starts to pull the sister chromatids apart. At the end of anaphase a complete set of daughter chromosomes is found each pole.

Anaphase I Sister chromatids remain attached. But homologous chromosomes move apart to opposite poles

Types of Reproduction

Sexual

Asexual

Occurs in

Humans, animals, plants, fungi.

All Organisms

Function

Genetic diversity through sexual reproduction.

Cellular reproduction and general growth and repair of the body.

Cytokinesis

Occurs in Telophase I and in Telophase II.

Occurs in Telophase

Karyokinesis

Occurs in Interphase I.

Occurs in

Discovered by

Oscar Hertwig

Walther Flemming

Mitosis

  • Mitosis is a continuum of changes but biologists like break down the stages of mitosis into four main stages, prophase, metaphase, anaphase and telophase.
  • The focus in this class is on an understanding of the process and not a memorization of phases.
  • The only phase name you will need to remember is metaphase.
  • In mitosis the nuclear membrane is broken down, spindle fibers (microtubules) attach to the chromatids at the centromere and pull apart the chromatids.
  • When the chromatids reach separate ends of the cells the spindle fibers disintegrate and a nuclear membrane rebuilds around the chromosomes making two nuclei.
  • Each nucleus is identical to the original nucleus as it was in G1.

Meiosis

  • Meiosis is the form of nuclear cell division that results in daughter cells that have one half the chromosome numbers as the original cell.
  • In organisms that are diploid, the end result is cells that are haploid. Each daughter cell gets one complete set of chromosomes, i.e., one of each homologous pair of chromosomes.
  • In humans this means the chromosome number is reduced from 46 to 23.
  • The only cells that undergo meiosis will become sperm or eggs.
  • The joining together of a sperm and egg during fertilization returns the chromosomes number to 46.
  • Cells that undergo meiosis go through the cell cycle including the S phase so begin the process with chromosomes that consist of two chromatids just as in mitosis.
  • Meiosis consists of meiosis I and meiosis II. In meiosis I homologous chromosomes are separated into different nuclei.
  • This is the reduction division; chromosome number is cut in half. Meiosis II is very similar to mitosis, chromatids are separated into separate nuclei.
  • As in mitosis, it is spindle fibers that “pull” the chromosomes and chromatids apart.
  • The end result of meiosis is four cells, each with one complete set of chromosomes instead of two sets of chromosomes.

Conclusion

The difference between Mitosis and Meiosis is quite apparent. They are two very different processes that have two different functions. Mitosis is required for genetic variation and continuity of all living organisms. Meiosis, on the other hand is focused on cellular growth and repair of the body.

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